A psychological trait described with the verb ser is considered more stable than one expressed by using estar (Heyman & Diesendruck, 2002). In order to establish whether ser/estar verbal forms affect inferences about psychological traits, 2 studies were carried out on school children in different developmental levels (N = 62, 7 and 12 years) and university students (N = 108), monolingual speakers of Peninsular Spanish, from medium socioeconomic status, resident in Madrid, Spain. In both studies participants were randomly assigned to one of 2 experimental conditions (ser and estar) and responded to an inference task which consisted of the description of psychological characteristics and behaviors associated with them. Factorial and repeated measures analysis of variance were performed. Only the adults and older children inferred that the traits described with ser were more stable than those expressed with estar. The younger children inferred that the traits were stable in both experimental conditions. The effect of the linguistic distinction on inferences is significant, but should be interpreted bearing developmental differences in mind.